Open source project to develop geopolymer cast stone construction

Imhotep’s Formula to Make Limestone Blocks

Imhotep had two different chemical formulas: a very simple one for the casting of the limestone core blocks, and another one to produce the high quality stones of the exterior layer. When all the blocks of the core were set in place, a layer of casing was applied. This meant preparing a more sophisticated type of mold to produce inclined limestone blocks following the slope of the pyramid, adding new ingredients to the mixture to yield a higher quality stone.

1. SOFT LIMESTONE
To build the Step Pyramid, Imhotep located a quarry of soft limestone, just one kilometer from the construction site to provide the raw material he needed to cast millions of modular stones. Soft limestone can be easily disaggregated either under pressure or by diluting it in water.

Shallow canals were dug in the soft limestone along the Nile, forming ideal basins for producing large quantities of muddy limestone. Imhotep’s men began disaggregating the clayish soft rock with its water, until the lime and the clay separated, forming a mud with the fossil shells at the bottom.

2. NATRON SALT
Next, a substance called Natron salt (sodium carbonate) was poured in. Salt is a very reactive substance that has a petrifying effect, which is why it is used to avoid the putrefaction of organic tissue (mummification). Natron is found in very great quantities in the desert and in Wadi-El-Natron.

3. LIME
More lime, the mineral which binds, was added. Lime is a powdery residue obtained by burning and reducing to ashes sedimentary rocks such as limestone and dolomite. The fire oxidizes and converts the rocks into a powdery residue, and that is lime. The ashes of plants are also rich in lime and the priests established the custom of receiving ashes from cooking fires from all over Egypt, to add them to the mixture.

4. CAUSTIC SODA
Lime mixed with natron and water produced a third substance, a much more corrosive one, that sparks off a strong chemical reaction and transforms other materials. The water dissolved the Natron salt and put the lime in suspension, forming caustic soda. Caustic Soda is the catalyst Imhotep needed to trigger off a powerful chemical reaction, one which would produce the fast integration of silica and alumina.

This question goes to the heart of what this blog is about. You’re right about the expense if you buy commercially available processed products. What we hope to do is replicate what was done thousands of years ago. They didn’t buy anything. They used what was locally available — loose limestone, natron salt, etc. We’re trying to pull together various recipes so people can use what’s nearby and inexpensive. Things like crusher fines (the powder that’s washed off crushed gravel) come to mind. We’re also exploring weaker materials that are probably “good enough” for many. Options like caliche, Alker technology and Low Strength Stone-like Material for Rural Areas https://geopolymerhouses.wordpress.com/2011/06/15/low-strength-stone-like-material-for-rural-building/ may work for you.Did you see the article where an ancient civilization built with glutinous rice? https://geopolymerhouses.wordpress.com/2011/06/23/ancient-bricks-of-sand-glutinous-rice-and-rice-hulls/ We’ve had lots of articles on waste materials — fly ash, slag, rice hull ash, bagasse ash and other industrial wastes. There’s also cast earth and poured earth. Some stories (blog posts) have reported on geopolymer made with 100% fly ash or 100% waste materials.

This open source blog is a journey. We’re not there yet. The strongest, most durable geopolymer products are pricey commercial products. They’re more sustainable than Portland because they create 80% less carbon dioxide, last longer, etc. But they’re out of reach price wise for many. Sometimes these products cost even more than Portland cement. It’s convenient to have off the shelf products we can utilize, but my real dream is to perfect simplified methods of making cast stone houses. Almost every day I read of ancient stone monoliths that were probably built with geopolymer and it gives me even more determination to figure out how it was done. What we really need now is a dedicated group to actively engage in testing and report the results. I’m slowly moving toward acquiring local materials for testing, but I’m extremely busy and can’t do as much as I’d like. This has to be a group effort.

Did you look up these prices from online sales for small quantites? Limestone should be something like $20 per pickup truck load. If it isn’t available locally, then build with something else. They used limestone because they had tonnes of it for the digging. If you have some other mineral (sand, feldspar, granite, caliche, whatever), use that instead.

Hydrated lime [Ca(OH)2] is just a few dollars for 50lbs wherever they sell cement and lime. CaO is not necessary and would be tough to get.

I can get soda ash (which is NOT sodium bi-carbonate, it is sodium carbonate which is different) for $12 per 50lbs.

Please note that this method also requires an alumino-silicate like kaolin which may or may not be present in the limestone or other mineral. one would have to experiment to find out. It is not in sand however.